Jonti

The balance temperature will be specific to the particular house and will depend on its fenestration, orientation, the weather (cold/sunny or freezing fog) and by no means least, the lifestyle of the occupants.

No way can the internal gains from a family of 4 living the passive house lifestyle meet the heat losses during the coldest weather.

We are involved in the design of 8 Passivhaus certified homes and the heat losses are around 1,300 Watts at -3 degC external ambient & 20 degC average internal. I would expect incidental gains for a family of 4 at no more than 700 Watts. Without solar input or additional heating the space temperature could in theory drop to

(-3) + (700/1300 x 23) = 9.4 degC.

For this to happen the outside temperature would have to stay at a diurnal average of -3 degC or less for several days with no solar gains - but more extreme conditions than this were experienced in Dec 2010.

We have therefore allowed for electric heating and PV. I would love to try solar heating on this project but our Client does not have the budget.

I've haven't seen Passive Houses get any colder than 16 degrees when unoccupied in winter, when its really cold there's plenty sun, when its overcast the temperature is rarely below 5-7 degrees.
My brother went away for a week the winter before last which was the really cold one (-15C), his brother in law collected him from the airport, when he got back home his brother in law walked into the house and said "You left the heating on!" The heating had been off for a week.

Hi Gary, what construction method will you use, where are you building, will you cover the complete roof with PV and what was the cost you got for Solar Thermal space heating?

GaryB, Like VH, I'm surprised by your very low prediction. Internal gains of 700 W less the heat from four people leaves about 300 W, which seems pretty low for lighting, cooking, bathing, TV & computers etc. Where does the 700 W come from? What does PHPP use (I don't have it in front of me)?

FWIW, Hockerton remains habitable. I don't know whether they had to do anything special in Dec 2010.

Sorry, forgot to add for the 8 units:

DER: -0.97
SAP: 102
Code Level: 5
Predicted EPC: A
Space heating requirement: 847.79 kWh pa
Energy Performance: 9.9 kWh/m2 pa

Posted By: djhFWIW, Hockerton remains habitable. I don't know whether they had to do anything special in Dec 2010.

I asked Liz Lainé (Hockerton resident) on Twitter. She replied:

@ed_davies Some Hockerton homes used top up heating in winter 2010, generally due to illness or home working (still for long periods) 1/2

(Not sure what that “1/2” is about - if she meant to post a second tweet or about half the houses needed top-up heating.)

https://twitter.com/TreadingLightly/status/263048256077062147

Edit to add: she says the “unheated” (i.e., not specifically heated) houses dropped to 16 °C. That's very consistent with what I was told by another resident: that the houses get down to 17 °C in a typical winter.

Posted By: eniacs I feel i have covered this by using the available space to capture as much solar as possible for the pool. I feel the extra needed to add a panel for water heating just doesnt justify the cost savings

Sorry for late reply, only just joined and reading past posts, hopefully of some interest or to others in future

I had a pool at a previous house 20 years ago. I was young and hardier; pool was outdoor heated by solar. We used it for the core of the summer only. The solar collector was equivalent to miles of black hosepipe back then. I wouldn't have an "outdoor" pool in the UK again.

We now have a pool with a uPVC enclosure, and half a dozen decent solar collectors. Before the solar was installed we rarely needed to heat the pool in summer, inside the enclosure was 90F and upwards from May onwards.

Our Solar Panels heat a thermal store, for DHW, and any surplus is dumped into the pool. The pool season for us is from Easter school holidays to Winter term half term. We need a lot of heat over the course of several days in March to get the pool up to temperature (pool is around 15C when I start heating it in Spring, and there is 100 cu.m. of water to raise by 15C - it takes a fair few kWh), and to keep it there until some time in April or May when the outdoor temperature rises (which it typically does all-of-a-sudden and then stays there, but the start date is not predictable) after which is mostly keeps itself warm.

We then heat again to extend the season to get to the Winter half-term (and in some lousy years, like this one, we don't bother). Other than that there is the occasional "dull" spell - Solar might be enough to tide over, but like all things Solar the need is only when the weather has been dull / cold, so a bit mutually exclusive, and we tend to have weekends with friends coming where the instruction is "pool must be hot enough" and if the weather doesn't oblige the boiler has to instead.

There isn't enough sun to generate the heat at the ends of the season, and a plastic tunnel [or similar is essential IMHO] over the pool will do the job during the core of the summer- and keep the leaves out, and keep any wind-chill off the swimmers which, in the case of kids, means they stay in all day long - bonus!

I chose my solar panels [sized] for Spring and Autumn - so that we would have DHW then without needing to fire up the boiler, and in the knowledge that if they generated excess heat in summer it would be dumped into the pool. We largely achieve that in practice (although this year's kWh YTD are a good 25% below the average for the previous years we have had it - so there will be years where you need something other than Solar, and in my experience at Start / End of season too).

My Solar Thermal panels would not generate enough heat for DHW in Winter - lucky to get a couple of kWh a day in Winter (and that is offset by the slug of cold water that comes back before the hot starts flowing)

Posted By: Krispya plastic tunnel [or similar is essential IMHO] over the pool will do the job during the core of the summer- and keep the leaves out, and keep any wind-chill off the swimmers

I believe that a floating cover over the pool itself will conserve a lot of heat. Mostly by reducing evaporation although it may also insulate a bit.